The foot moves in three directions: (1) sagittally, in an up and down direction similar to the pitch of an airplane; (2) transversely, in a rotational direction similar to the roll of an airplane; and (3) along the coronal or frontal plane in a left-right direction, similar to the yaw of an airplane. The central component of this motion is the talus bone, located below the tibia-fibula, and above, and anterior to the calcaneous (heel bone).
During physical activity, adverse movement or alignment of the foot translates through a person's entire kinetic chain, affecting the knee, hips, and lower back. For example, poor alignment with ground reaction during running can cause stress and induce pain in the knees, hips, and lower back. The optimal alignment during movement is for the calcaneus to remain in a neutral position and the talus to move in a midline position with the knee without excess internal or external rotation. The alignment of the talus and knee can be tested by having a person bend his or her knees. If the talus is optimally aligned with the knee, a plumb line applied to the center of the knee will fall directly over the second metatarsal ray of the foot when the person's knee is slightly bent. When most people bend their knees, however, their knees will fall medially or laterally away from the second metatarsal ray of the foot.
If the talus rotates adversely, the rest of the foot must compensate accordingly. Inward (medial) rotation of the talus causes the hindfoot to compensate with an outward (valgus) movement of the calcaneus, depression of the midfoot, and abduction of the forefoot. As a simple explanation, a foot may pronate, though excessive internal rotation of the talus causes anatomical complications much worse than simple pronation. An outward (external) rotation of the talus also requires compensation by the rest of the foot in the reverse directions—the hindfoot moves inward (varus), the midfoot arches (elevates), and forefoot adducts—that can be simply described as the foot supinating.
These compensatory movements induce strain in the entire kinetic chain of the body, and usually other parts of the kinetic chain compensate for such misalignments. For example, the knee can be pushed medially or laterally, or various parts of the hip can shift to compensate for the strain. Over time, this strain can cause medical conditions such as (but not limited to) plantar fasciitis, Achilles tendonitis, posterior tibialis tendonitis, knee pain with ligamentous and tracking problems, bunions, and hip pain. Positioning and stabilizing the tri-planar motion of the foot during movement can reduce the adverse compensatory movements of the foot and other parts of the kinetic chain, thus reducing (or even eliminating) the corresponding medical problems.
Various prior art solutions for stabilizing the foot are already known. Many types of braces and bandages exist that can be wrapped around a foot, though these corrective devices are often bulky and interfere with the proper fit of a shoe. Gel pads and shoe inserts can be added to the insole of a shoe, but these inserts also can interfere with fit and performance of the shoe. Also, these solutions add weight and bulk to a person's foot. None of these approaches acts simultaneously to stabilize the foot at the three planes described above.
Some shoe manufacturers have developed mechanisms or improved shoe designs for reducing the occurrence of injuries or medical conditions like those described above. For example, running or basketball shoes can include modified flex grooves in the sole, reinforcing laminate mid-sole designs, or pockets of air or gel to provide greater cushioning. However, none of these known solutions stabilizes motion of the foot along all three planes identified above.
The inventor of the inventive subject matter described has attempted to address the aforementioned problems on an individualized basis by creating custom orthotics that make a tri-planar correction. The customized orthotics are inserted into conventional shoes. Unfortunately the orthotics approach while helpful does not provide an optimized solution because of the inherent incompatibilities of combining a custom orthotic with a conventional shoe. For example, the orthotic adds extra height and bulk to a shoe, which can cause instability for the wearer and decreased efficiency in athletic and sports activities. The orthotic may also decrease the volume of the foot compartment of a shoe causing a poor, uncomfortable fit. Pressure points may also occur from the stitching and design of the shoe. Further conventional shoes may have conformations for their uppers and/or sole units that counteract the corrections that an orthotic are intended to make. However, because of the individualized nature of orthotics, there still remains a need for off-the-shelf shoes, as well as custom shoes, that provide an integrated system for tri-planar corrections.
Accordingly there is a substantial need for footwear systems that adjust or stabilize the tri-planar motion of a foot.